1. Field of the Invention
The present invention relates to a ram driving device for moving a ram up and down, which is suitable for a machine such as a press machine, bending machine, etc.
2. Description of the Related Art
Some examples of the conventional ram driving device for moving a ram up and down in a press machine such as a punch press machine will be first described herein below.
As a first ram driving device, there exists such a device that a hydraulic cylinder having a piston linked with a ram is actuated by a hydraulic circuit arrangement.
As a second ram driving device, there exists such a device that a horizontal drive axle is rotatably provided in a frame of a press machine; a rotational motion of the drive axle is converted into the ram up-and-down motion by a motion converting mechanism; and a drive motor is linked with the drive axle via a clutch brake to rotate the drive axle. Here, the motion converting mechanism is usually composed of an eccentric portion attached to the drive axle eccentrically, and a connecting rod one end of which is pivotally linked with a ram and the other end of which is also pivotally linked with the eccentric portion.
As a third ram driving device, there exists such a device that a drive axle and a motion converting mechanism are provided in the same way as with the case of the second example. In this Example, however, the drive axle is directly linked with a servomotor, without use of any clutch brake.
In the above-mentioned conventional ram driving devices, however, there exist the following problems:
In the first example, since the ram is moved up and down by the hydraulic source, the cost required for the maintenance of the hydraulic cylinder and the hydraulic circuit arrangement is relatively high. In the second example, although the maintenance cost is not high, since the moving stroke and the speed of the ram cannot be controlled freely, it is impossible to apply the same ram driving device to various press machines of different moving strokes and speeds. Further, in the third example, since the drive axle is rotated by the servomotor, although the moving stroke and the speed of the ram can be changed freely, since the press power of the ram is relatively small, there exists a problem in that the servomotor cannot be used for a press machine which requires a large press power.